The present invention relates to friction stir welding and, more particularly, relates to friction stir welding tubular members.
Friction stir welding is a relatively new process using a rotating tool having a pin or probe and a shoulder to join two workpieces in a solid state or to repair cracks in a single workpiece. For example, such a process is described in U.S. Pat. No. 5,460,317 to Thomas et al., the contents of which are incorporated herein by reference. As illustrated in FIG. 1, during friction stir welding, the probe 10a of the rotating tool 10 is plunged by a friction stir welding machine into a workpiece or between the faying faces of two workpieces 12 to produce the required resistance force to generate sufficient frictional heating to form a region of plasticized material. The tool 10 is typically tilted at an angle relative to the workpiece or workpieces 12 such that the trailing edge of the tool shoulder 10b is thrust into and consolidates the plasticized material created as the tool is moved along a path defined by the weld joint to be formed. Upon cooling of the plasticized material, the workpieces are joined along the weld joint. The magnitude of force exerted by the friction stir welding tool must be maintained above a prescribed minimum in order to generate the required frictional heating.
The force exerted by the friction stir welding tool produces a homogeneous weld joint having approximately 75% of the mechanical properties of the parent material, as opposed to approximately 50% for fusion weld joints. At present, however, the friction stir weld process is applied almost exclusively in straight-line welds. When joining workpieces having complex, curvilinear geometries, such as tubular members, moving the friction stir welding tool about the circumference of the workpieces and controlling the depth of the probe in the workpieces become problematic. In addition, when joining tubular members, such as adjacent lengths of tubing, it is also necessary to maintain the tubular members in coaxial alignment, which can be particularly difficult when applying a force of sufficient magnitude to generate the required frictional heating to form a region of plasticized material.
Thus, there is a need for an improved friction stir welding device for forming friction stir weld joints in workpieces having curvilinear geometries, such as tubular members. The welding device should be capable of effectively supporting the tubular members during welding. Additionally, the welding device should be capable of effectively translating a friction stir welding tool about the circumference of the tubular members and should be easily adaptable to varying tube geometries and sizes.
The present invention provides an apparatus for forming a weld joint between abutting ends of first and second tubular members. The welding apparatus includes a support ring defining an aperture therethrough. The support ring has first and second sides defining a channel therebetween. The first side of the support ring defines a plurality of supports spaced about the circumference of the support ring, each of which defines a gripping surface for contacting at least a portion of the exterior surface of the first tubular member to thereby secure the abutting end of the first tubular member at least partially within the aperture of the support ring. The second side of the support ring defines a plurality of supports spaced about the circumference of the support ring, each of which defines a gripping surface for contacting at least a portion of the exterior surface of the second tubular member to thereby secure the abutting end of the second tubular member at least partially within the aperture of the support ring adjacent to, and coaxially aligned with, the abutting end of the first tubular member. According to one embodiment, the first-side and second-side supports are slidably mounted to the support ring. According to another embodiment, the apparatus includes a plurality of actuator assemblies secured to the support ring. Each of the actuator assemblies is in operable communication with one of the supports for urging the support toward and away from the corresponding tubular member to thereby accommodate different diameter tubular members. According to still another embodiment, each of the first-side and second-side supports comprises a primary support, an alignment clamp pivotally attached to the primary support, and an actuator assembly in operable communication with the alignment clamp. In one embodiment, the actuator assembly is selected from a group consisting of a pneumatic actuator arm or a hydraulic actuator arm.
The welding apparatus includes a least one friction stir welding tool, which is movably and rotatably mounted within the channel defined by the support ring and which projects toward the abutting ends of the first and second tubular members. The welding apparatus also includes means, in operable communication with the at least one friction stir welding tool, for rotating the at least one tool, and means, in operable communication with the at least one friction stir welding tool, for moving the at least one tool about the abutting ends of the first and second tubular members to thereby form the weld joint. According to one embodiment, the rotating means comprises a rotatable spindle and a motor in operable communication with the spindle. According to another embodiment, the moving means comprises a drive assembly and a motor in operable communication with the drive assembly, and wherein the drive assembly is selected from a group consisting of a belt drive or a gear drive.
According to another embodiment, the welding apparatus includes at least one friction stir weld head movably mounted within the channel of the support ring. The at least one weld head includes a motor having a rotatable spindle and a friction stir welding tool rotatably mounted to the spindle of the motor. The welding apparatus also includes means, in operable communication with the at least one friction stir weld head, for moving the at least one weld head along a path defined by the channel of the support ring such that the rotating friction stir tool moves along a path defined by the abutting ends of the first and second tubular members to thereby form the weld joint. In one embodiment, the moving means includes a drive assembly and a motor in operable communication with the drive assembly, and wherein the drive assembly is selected from a group consisting of a belt drive or a gear drive.
According to still another embodiment, the welding apparatus includes means, in operable communication with the at least one friction stir welding tool, for urging the at least one friction stir welding tool toward and away from the abutting ends of the first and second tubular members in order to modify the force exerted by the friction stir welding tool on the abutting ends of the first and second tubular members. In one embodiment, the means for urging the at least one friction stir welding tool comprises a drive assembly and a motor, in operable communication with the drive assembly, and wherein the drive assembly is selected from a group consisting of a belt drive or a gear drive.
The present invention also provides a method of welding the abutting ends of first and second tubular members, including the steps of inserting the abutting end of a first tubular member into an aperture defined by a support ring. A plurality of supports defined by a first side of the support ring are moved into contact with at least a portion of the surface of the first tubular member such that the abutting end of the first tubular member is at least partially secured within the aperture defined by the support ring. The abutting end of a second tubular member is inserted into the aperture defined by the support ring such that the abutting end of the second tubular member is adjacent to, and coaxially aligned with, the abutting end of the first tubular member. A plurality of supports defined by the second side of the support ring are moved into contact with at least a portion of the surface of the second tubular member such that the abutting end of the second tubular member is at least partially secured within the aperture defined by the support ring and in coaxial alignment with the abutting end of the first tubular member. According to one embodiment, the moving steps comprise moving a primary support into contact with at least a portion of the surface of the corresponding tubular member and, thereafter, moving an alignment clamp into contact with at least a portion of the surface of the corresponding tubular member. According to another embodiment, tooling is positioned adjacent to the abutting ends of the first and second tubular members opposite of the friction stir welding tool to support the abutting ends of the first and second tubular members during friction stir welding.
The method also includes inserting at least one rotating friction stir welding tool into the abutting ends of the first and second tubular members to thereby join the abutting ends of the first and second tubular members by friction stir welding. According to one embodiment, the at least one rotating friction stir welding tool is moved through the first and second tubular members along a path that traces the abutting ends of the first and second tubular members to thereby form a continuous joint about the circumference of the first and second tubular members. According to another embodiment, the at least one friction stir welding tool is withdrawn from the abutting ends of the first and second tubular members after moving the at least one friction stir welding tool through the first and second tubular members.
Accordingly, there has been provided a welding device and associated method of manufacture for forming friction stir weld joints in workpieces having curvilinear geometries, such as tubular members. The welding device is capable of effectively supporting the tubular members during welding. Additionally, the welding device is capable of effectively translating a friction stir welding tool about the circumference of the tubular members and is easily adaptable to varying tube geometries and sizes.